1. Field of the Invention
This invention relates to separation devices, more specifically to a separation device for the quick separation between a solid material and a gaseous material from a mixture thereof.
2. Prior Art
There are known a reaction system in which a solid particle as a catalyst or heat medium is brought into contact with a reactant A fluidized bed type reactor is a typical example of such reaction system which reactor is classified into one utilizing a dense-phase fluid bed (bubbles-fluid bed) and the other utilizing a high-velocity moving bed The high-velocity moving fluid bed is used for a reaction in which a solid and a gas must come into contact for a short period of time. Currently, there has been mainly employed an upward flow-type high velocity moving bed reactor called "riser" in a fluid catalytic cracking (F.C.C) apparatus used for the production of a gasoline from a feedstock such as a heavy oil. This reactor is capable of reducing contact time due to an improvement of a catalyst in ability, leading to an enhancement of selectivity of a final product and depression of excessive cracking reaction.
One problem faced by a conventional high velocity fluidized bed reactor is the need to obtain a quick separation of fine catalyst particles form from reaction vaporized product leaving a riser reactor in a system. Therefore, an improvement of separation device has been demanded. In order to deal with such a problem, it has been proposed to use a separation system so called "closed cyclone" disposed in close proximity of the discharging end of riser in an FCC apparatus for producing gasoline from heavy oil as disclosed in U.S. Pat. Nos. 5,552,120 and 5,538,623.
It becomes more important to obtain the quick separation between solids and reaction gaseous material at the discharging port of a reactor particularly when in an FCC apparatus Light olefin is intended to be produced with a short contact time process effected for 0.1 to 1.5 second. In such a short contact reaction, the existing separation device such as a cyclone invites a reduction in yield of the reaction product and coke deposition because gaseous materials have a longer residence time in a reactor than in the separation device, leading to further reaction progressed in the separation device
Instead of separating a catalyst from the mixture using a separation device for a short contact reaction, the further reaction can be avoided by cooling the mixture of the reaction product and a catalyst quickly at the discharging end of a riser. However, in an FCC apparatus for producing gasoline from heavy petroleum fractions, the catalyst is regenerated by heating at elevated temperatures to use for reaction as heat medium. Therefore, this idea is not preferable in terms of heat efficiency.
After all, the effective method for avoiding excess reaction is the quick separation between catalyst particles and reaction gaseous materials at the outlet port of a reactor. If the catalyst particles can be separated mostly but not completely, the catalyst become less contributive in effecting the reaction in the following cyclone even if they reside longer therein. If the reaction in the cyclone can not be ignored, the rapid cooling may be effected at the inlet port of the cyclone so that the catalyst can be regenerated without affecting heat efficiency of the apparatus.
U.S. Pat. No 3,074,878 discloses a process for quick separation of a mixture at the outlet port of a reactor. In this process, a solids-gas mixture passing downwardly is deflected to one side of a tubular reactor by a baffle element disposed therein and sprayed transversely with a gas from the other side. However, the spraying angle can not be altered more than 90 degrees, resulting in poor separation efficiency. Furthermore, the baffle element is prone to abrasion due to direct impact with the solids.
Another example of the quick separation is disclosed in Japanese Patent Publication No. 60-18447 in which a rectangular chamber is disposed horizontally with respect to a downflow or upflow type reactor. After the mixture flows into the chamber from one end thereof and changes the flow direction at an angle of 90.degree., the catalyst particles and the reactant gaseous material are removed from the other end of the chamber in the upward and downward directions, respectively. However, as the flow of the mixture in the chamber is extremely turbulent, the separated catalyst fails to flow toward the discharging port of the chamber efficiently and thus tends to be whirled upwardly in the chamber, resulting in a reduction of separation efficiency. This tendency becomes more remarkable as the mixing ratio of the catalyst in the mixture increases.
In a process in which contact time must be shortened to improve selectivity of a reaction product, it is absolutely necessary to increase the recycle rate of a catalyst for compensating for the reduction of conversion ratio due to the short contact time. Taking this background into account, there has been demanded a high-speed separation device which can effect a quick separation between catalyst particles and reaction gaseous material from the mixture thereof in the a large mix ratio of the particles.
The term "separation efficiency" used herein designates the ratio of the solids separated out from the mixture supplied into the separation device, i.e. the ratio of the solids discharged out from the outlet of the separation device which ratio is represented by the following formula: EQU Separation Efficiency (%)=(Weight of the solids withdrawn from the discharge port)/(Weight of the solids supplied into the separation device)
The term "mix ratio" used herein is a numerical value derived by the following formula: EQU Mixing ratio=(Weight of solids)/(Weight of gaseous reaction product)